* Rebels, government have met mediators, not each other yet
* More than 1,000 people killed since violence began
* Western powers, neighbours fear civil war in South Sudan
By Aaron Maasho
ADDIS ABABA, Jan 4 (Reuters) - South Sudanese rebels and government negotiators will hold their first face-to-face talks on Sunday, after several days of delay, to thrash out a ceasefire deal and end ...